240 and 310.15

Status
Not open for further replies.
D

Dale001289

Senior Member
Location
Georgia
We see a lot of European equipment being crammed into domestic US projects. I have a vendor panel with 1pole, 32A CB's at 120VAC. The contractor ran #10 Awg cable to the CB's. Is this permissible? NEC shows maximum for #10's as 30A.
 
Dale001289 said:
We see a lot of European equipment being crammed into domestic US projects. I have a vendor panel with 1pole, 32A CB's at 120VAC. The contractor ran #10 Awg cable to the CB's. Is this permissible? NEC shows maximum for #10's as 30A.
Click to expand...
Depends...

What does the circuit power?

It could be fine for applications listed in Table 240.3. For example, it may be fine for powering a motor.
 
Powers up a vendor control panel off a 120/208V panel board. Known Load is light but future loads are unknown


Sent from my iPhone using Tapatalk
 
What is the terminal temp rating? Domestic equipment is commonly 75C so #10 THHn/THWN 2 copper wire rated to 35 Amps so itd be fine.

Sent from my SM-G935P using Tapatalk
 
richie921 said:
What is the terminal temp rating? Domestic equipment is commonly 75C so #10 THHn/THWN 2 copper wire rated to 35 Amps so itd be fine.

Sent from my SM-G935P using Tapatalk
Click to expand...

Not sure what the strip is rated. However I believe the cable its still restricted to 30A per 310.15(B)(16) and 240.4(D)(7), regardless of the Insulation.
 
No, 310.15(B)(16) lists ampacity based on Terminal temperature rating,insulation type and assumes no more than three current carrying conductors in a Raceway. The most common column is 75 C which would give number 10 THHN a 35 amp rating ( the insulationof THHN is actually a 90c insulation rated at 40 amps but you're restricted by the terminal temperature rating)

Sent from my SM-G935P using Tapatalk
 
I should actually rephrase that the table does not specifically address terminal temperature rating but you have to use that when selecting the column that you go by, regardless of the insulation rating

Sent from my SM-G935P using Tapatalk
 
richie921 said:
I should actually rephrase that the table does not specifically address terminal temperature rating but you have to use that when selecting the column that you go by, regardless of the insulation rating. You use whichever is lower the rating of the insulation or the terminal



Sent from my SM-G935P using Tapatalk
Click to expand...
 
richie921 said:
No, 310.15(B)(16) lists ampacity based on Terminal temperature rating,insulation type and assumes no more than three current carrying conductors in a Raceway. The most common column is 75 C which would give number 10 THHN a 35 amp rating ( the insulationof THHN is actually a 90c insulation rated at 40 amps but you're restricted by the terminal temperature rating
Click to expand...
The footnote...
**Refer to 240.4(D) for conductor overcurrent protection limitations.
Click to expand...
240.4(D)(7) in particular. :D
 
Maybe I read your initial question wrong. The 32 amp CB had number 10 wire ran TO them. I'm seeing that as feeding them and the question only being could 10 gauge wire legitimately be used with a 32 amp load and still be within its ampacity. 240 obviously deals with overcurrent protection feeding the conductor but from your initial post I read it as the CBs are the load on the conductor. In fact I think Dennis asked about what size breaker the number 10 was on. You're correct if the CBs in the control panel are protecting the number 10 and its not motor or ac or other "exemption" loads then yes you would be limited to 30 amps if the CBs are the load on the number 10, 32 amps is within its ampacity.

Sent from my SM-G935P using Tapatalk
 
richie921 said:
I should actually rephrase that the table does not specifically address terminal temperature rating but you have to use that when selecting the column that you go by, regardless of the insulation rating

Sent from my SM-G935P using Tapatalk
Click to expand...

The key is 240.D - ambient temperatures can vary dramatically, 30A represents a 'buffer' so to speak, see table 310.15(B)(2)(b). Look at industrial process Heaters in a Refinery, or high ambient temperatures due to extreme weather; here temps may go up to 115F therefore .85 x 35 =29.75A. This is why you're always restricted to 30A.
 
240.4 specifies ampacity limits AFTER any necessary adjustments for ambient or conductor count have been made. Not sure if that's what you mean. Sometimes typed discussions can be very aggravating because the wording and intent of the question may not always be clear through no fault of anyone it's just the limit of written communication as opposed to verbal

Sent from my SM-G935P using Tapatalk
 
richie921 said:
240.4 specifies ampacity limits AFTER any necessary adjustments for ambient or conductor count have been made. Not sure if that's what you mean. Sometimes typed discussions can be very aggravating because the wording and intent of the question may not always be clear through no fault of anyone it's just the limit of written communication as opposed to verbal

Sent from my SM-G935P using Tapatalk
Click to expand...

I certainly agree with the third sentence in your comment. Also, consider this; many times rating of the T'Strip or overcurrent device terminals are not known therefore, 240.(D)(7) applies - i.e. the 60C rating restricts you to 30A. See 110.14(C)(1).
 
Absolutely... but many times (though certainly not always) unknown ratings and that "assumption" are more for test-taking purposes where you may be given limited equipment information. As with most questions regarding the NEC the dynamic is very broad. What seems like a simple question turns to into being very involved. This question by the op is no different. He's got 32 amp CB's with number 10 running to it. So if you read that as the number 10 wire is the line then the primary overcurrent protection is in place and the rating of those still falls within the ampacity of the conductor. However if the 10 wire is protected by the 32 Amp CBS, then 240.4 comes into play UNLESS the load served is specified in table to 240.4 G as an exception. Have a headache yet? Lol

Sent from my SM-G935P using Tapatalk
 
Dennis Alwon said:
If the unit is fed with a 30 amp breaker then it is compliant as the 30 amp device will protect the wire
Click to expand...

Dale001289 said:
Perhaps, but the cable on load side of the 32A CB is also rated 30A - don't think this is 'kosher'.
Click to expand...
If the vendor panel's supply is via a 30A breaker and #10 Cu it does not matter that the load side #10 is protected via a 32A breaker as it is protected by the 30A supply breaker.
 
richie921 said:
Absolutely... but many times (though certainly not always) unknown ratings and that "assumption" are more for test-taking purposes where you may be given limited equipment information. As with most questions regarding the NEC the dynamic is very broad. What seems like a simple question turns to into being very involved. This question by the op is no different. He's got 32 amp CB's with number 10 running to it. So if you read that as the number 10 wire is the line then the primary overcurrent protection is in place and the rating of those still falls within the ampacity of the conductor. However if the 10 wire is protected by the 32 Amp CBS, then 240.4 comes into play UNLESS the load served is specified in table to 240.4 G as an exception. Have a headache yet? Lol

Sent from my SM-G935P using Tapatalk
Click to expand...

I believe the issue of 'presumptive' loads/temps/ratings etc were part of the estimating process vs test taking process - the worst-case scenario took precedence in this case.
 
Status
Not open for further replies.
Top